Research and development on nonaqueous electrolyte secondary batteries for use in applications such as mobile phones, hybrid or electric vehicles and home storage systems has been widely carried out in recent years.
Nonaqueous electrolyte secondary batteries used in such applications are required to meet high safety standards and have a long lifetime.
Among nonaqueous electrolyte secondary batteries, lithium-ion secondary batteries have attracted considerable attention for satisfying such high requirements. Especially on the rise is the development of lithium-ion secondary batteries structured to have a spinel-type lithium manganese oxide as a positive-electrode active material and a titanium compound as a negative-electrode active material.
However, lithium-ion secondary batteries using a titanium compound as a negative-electrode active material may cause a reaction gas to be formed when the electrolyte reacts with the negative-electrode active material during charging or the like. Such a reaction gas blocks migration of lithium ions between electrodes, thus lowering the cycle stability.
Considering the aforementioned problems, Patent Literature 1 proposes a secondary battery formed by using a spinel-type lithium manganese oxide for the positive electrode, to which lithium cobalt oxide is added.
According to the battery of Patent Literature 1, formation of gas in the battery is suppressed because of a lithium composite oxide having a layered crystal structure added to a spinel-type lithium manganese oxide.
Moreover, Patent Literatures 2˜4 are publications also related to the present invention.